Display screen or portion thereof with transitional graphical user interface



FIG. 1 is the first image of a sequence of a display screen or portion thereof with transitional graphical user interface showing our new design; and,

FIG. 2 is the second image thereof.

The subject matter in this patent includes a process or period in which an image changes into another image. This process or period forms no part of the claimed design.

The dashed broken line in the perimeter of the drawings illustrates a display screen or portion thereof and forms no part of the claimed design. The remaining dashed broken lines indicate portions that form no part of the claimed design. 

CLAIM We claim the ornamental design for a display screen or a portion thereof with transitional graphical user interface, as shown and described. 